Since the identification of the BRCA1 gene 10 years ago much has been learned about the role of the BRCA1 protein in cancer development. In particular, genetic and epidemiological approaches have informed about the spectrum of mutations that occur in the gene and the prevalence, penetrance, and phenotype associated with these mutations in various populations. Furthermore, advances have been made in understanding the environmental and genetic modifiers of cancer risk associated with BRCA1 mutations. In this review the current knowledge of the genetic epidemiology of BRCA1 is presented and the issues that still need to be addressed in this field are outlined.